SEASONAL RESPONSE OF SURFACE MOVEMENT AND HYDRAULIC HEAD IN THE GLACIAL LAKE AGASSIZ PEATLANDS, NORTHERN MINNESOTA

Instrument arrays consisting of nine GPS and three hydrologic-meteorologic stations were installed in the Glacial Lake Agassiz Peatland in northern Minnesota. GPS data, collected by attaching the GPS antennae to small trees to monitor the movement of the surfical peat, reveal strong seasonal changes in surface elevation that are synchronous with hydraulic head data. These data indicate that peat surface moves upward during the spring freshet when hydraulic head within the peat also increases. In 2009, these changes were largest at a fen site (10 cm) and near a drainage ditch (25 cm), and smallest at the bog crest (4 cm). At all but the bog site, surface elevation and hydraulic head drop through the spring, summer and fall. In contrast, the surface elevation at the bog site is relatively stable until late December when a significant snow event occurs and the bog surface rapidly drops about 4 cm while hydraulic head increases. The general surface elevation and hydraulic head response at these sites is punctuated by higher frequency changes that appear to be associated with precipitation events. We believe that some of the anomalous surface deflection and hydraulic head changes are associated with the release of biogenic gas and continue to explore our data to identify processes that corroborate or refute this hypothesis.